Rack base



FIG. 1 is a perspective view of a rack base showing my new design;

FIG. 2 is a front elevational view thereof;

FIG. 3 is a left side elevational view thereof;

FIG. 4 is a right side elevational view thereof;

FIG. 5 is a top plan view thereof;

FIG. 6 is a bottom plan view thereof; and,

FIG. 7 is a perspective view of the design in state of use.

The broken lines shown in FIG. 7 are for illustrating environment only and form no part of the claimed design. 

CLAIM The ornamental design for a rack base, as shown and described. 